1. Field of the Invention
The present invention relates to an optical disc playback apparatus, and more particularly, to an improved hybrid disc and a method and an apparatus for discriminating the same.
2. Description of the Related Art
A digital versatile disk (hereinafter, called "DVD" for short) playback apparatus can playback both a CD (compact disk) and a DVD. Thus, the DVD playback apparatus has a function of discriminating a type of the disc installed therein, to set a proper playback mode according to the disc type.
In discriminating the disc type, the DVD playback apparatus checks whether an installed disc is a DVD or a CD upon installation of the disc, and sets a proper playback mode according to the detected disc type. More specifically, upon installation of the disc, the DVD playback apparatus irradiates a laser beam for DVD/MMCD (Digital Versatile Disk/Multimedia CD) (hereinafter, referred to as a "DVD/MMCD laser beam" for short) having a wavelength of 650 nm on the surface of the disc, to read data recorded thereon. At this moment, if the data recorded on the disc is readable, the DVD playback apparatus recognizes the installed disc as a DVD and begins to read and playback the data recorded on the DVD. On the contrary, however, if the data recorded on the installed disc is unreadable, the DVD playback apparatus irradiates a laser beam for CD (hereinafter, referred to as a "CD laser beam" for short) having a wavelength of 780 nm on the surface of the disc to read the data recorded on the installed disc. If the data recorded on the disc is readable, the DVD playback apparatus recognizes the installed disc as a CD, and begins to read and playback the data recorded thereon.
However, unlike a general CD (i.e., read-only CD), a recordable CD may be damaged undesirably, when exposed to the DVD/MMCD laser beam with a wavelength of 650 nm. To prevent the recordable CD from being damaged by the DVD/MMCD laser beam, an improved DVD playback apparatus first checks whether the installed disc is a CD or not and thereafter, checks whether the installed disc is a DVD, if it is not the CD.
With an increasing demand for a multipurpose optical recording medium, a hybrid disc has been proposed which is compatible with both a CD playback apparatus and the DVD playback apparatus. Such a hybrid disc is applicable to a CD-ROM/DVD-ROM, a video-CD/DVD-video drive, a CD-DA (digital audio)/DVD-audio device, etc.
Referring to FIG. 1, the hybrid disc includes a poly-carbonate substrate having a diameter of 12 cm and a thickness of 1.2 mm. The hybrid disc includes a CD recording surface B positioned about 5 .mu.m below a label printed surface A, and a DVD/MMCD recording surface C positioned about 0.6 mm below the label printed surface A. The CD recording surface B has a reflection factor of about 70%, and the DVD/MMCD recording surface C has a reflection factor of about 30%. As a combined CD and DVD recording medium, the hybrid disc is recognizable as a CD in the CD playback apparatus, and as a DVD in the DVD playback apparatus. CD data is recorded on the CD recording surface B, and DVD data is recorded on the DVD/MMCD recording surface C.
Therefore, the CD playback apparatus irradiates the CD laser beam on the hybrid disc, to read data recorded on the CD recording surface B, and the DVD playback apparatus irradiates the DVD/MMCD laser beam on the hybrid disc, to read data recorded on the DVD/MMCD recording surface C.
However, in the case that the DVD playback apparatus first checks whether the installed disc is a CD or not as mentioned above, to prevent the CD from being damaged in the course of discriminating the disc type, the DVD playback apparatus may mis-recognize the hybrid disc as a CD by reading the data recorded on the CD recording surface B of the hybrid disc.